Impactor and paste feeder

ABSTRACT

A paste feeder for moving paste from a paste cartridge to a cavity in a patient&#39;s mouth is described. The paste feeder has a paste cartridge for holding a paste and a paste channel defining a cavity for holding the paste cartridge. The paste feeder also has a paste feeder tube, operatively connected between the paste channel and a dispensing tip. A ratcheting device of the paste feeder operatively connects to a plunger. The plunger moves the paste from the paste cartridge through the paste feeder tube to the dispensing tip in controlled incremental amounts.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 10/625,476 that was filed on Jul. 22, 2003 which claims priority of pending U.S. patent application Ser. No. 60/397,704 filed on Jul. 22, 2002 and entitled Impact Condenser Slurry Feeder.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to paste feeders in general. The present invention is described in the context of medical devices, particularly dental devices and practices.

DESCRIPTION OF THE RELATED ART

Several different types of dental restorative materials, primarily mercury-containing silver alloys (also known as silver amalgams), gold foils, and polymeric fillings, are currently placed in situ in the dental office. In contrast, ceramic and solid gold restorations require laboratory preparation.

Currently, the predominant dental restorative or filling material is mercury-containing silver alloy because of its relative convenience and longevity. Unfortunately, mercury-containing silver alloy contains approximately 50 percent weight mercury, which has serious negative health consequences for patients, dental practitioners and the environment.

When silver amalgams are administered, patients and dental practitioners are exposed to mercury. When mercury-containing alloy fillings are removed, the patients can once again be exposed to mercury vapor. Further, these mercury-containing alloy fillings are discarded as waste, which causes serious environmental concerns as mercury waste can enter public water treatment plants.

The advantages of mercury-containing silver amalgam are its high strength, the bactericidal properties of its silver oxide, its low cost, and its suitability for an efficient in-office restoration. While a pure silver restoration exists (U.S. Pat. No. 5,711,866 to Lashmore) which meets the present need for a mercury-free alternative to mercury-containing amalgam, the drawbacks of the prior art precluded its commercialization. The present invention addresses and resolves these drawbacks and thus meets the existing need for a mercury-free restoration that can be successfully commercialized and that provides in one system a combination of advantages (superior safety, efficiency, effectiveness, convenience, ease of proper installation, and lower cost) that is not provided by any one commercially available alternative.

SUMMARY OF THE INVENTION

The present invention consists of an impactor, a paste feeder, thermally sealed disposable cartridges containing restorative paste, and a power supply. The impactor uses a solenoid-driven hammer to strike an anvil tip which contacts the restoration paste. The anvil tip welds the paste into a solid metal restoration in the cavity of a patient's tooth. The paste feeder can either be incorporated into the handle of the impactor or it can be part of a separate instrument. The cartridges contain a restoration paste of pure silver and dilute 2% tetrafluoroboric acid (HBF₄).

The purpose of this invention is to provide a safer, more precise, more effective, more efficient system for the placement of an in situ dental restoration that is free of mercury, gallium, and indium and that is inherently safer, better performing, longer lasting, easier to install properly, and more convenient than a silver-mercury restoration.

The present invention also provides a means of reducing the amount of mercury waste entering wastewater treatment systems, reducing waste water treatment requirements for dental practitioners, and reducing the amount of mercury waste released into the environment.

The present invention solves at least three problems in the prior art: (1) the time required to install the restoration, (2) the low density of the restoration when installed by hand instruments, and (3) the need to remove the activating solution during the condensation. The present invention solves these three problems by offering a means for automatically and rapidly injecting a paste of silver and dilute 2% tetrafluoroboric acid into the cavity of a patient's tooth and rapidly impact condensing the silver paste into a highly dense in situ restoration. With alternative embodiments of the subject impactor, gold foil or gold alloy powder is impact condensed into a gold restoration. The high density of the materials and short time to impact condense them solves the major problems in the prior art.

The present invention also has applications beyond that of dental restoration. For example, the impactor has a solenoid that can be scaled up and applied to the pressing of powders in larger powder metallurgy dies to mass-produce parts. The advantage of compacting powders with a repetitive impacting solenoid system is that very high impulse loading is obtained with relatively low static loads, resulting in parts of much higher density and lower part expansion in the die.

In an alternative embodiment of the present invention, the impactor is battery-powered making it ideal for veterinary and military applications and for general field use.

In another alternative embodiment, a paste feeder moves paste from a paste cartridge to a cavity in a patient's mouth. The paste feeder has a paste cartridge for holding a paste and a paste channel defining a cavity for holding the paste cartridge. The paste feeder also has a paste feeder tube, operatively connected between the paste channel and a dispensing tip. A ratcheting device of the paste feeder operatively connects to a plunger. The plunger moves the paste from the paste cartridge through the paste feeder tube to the dispensing tip in controlled incremental amounts.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will be better understood by reading the following detailed description, drawings, and claims, wherein:

FIG. 1 is a side view of an impactor having a head and a handle with a cross-sectional view through the head according to the present invention;

FIG. 2, an enlarged, exploded view of the head of the impactor shown in FIG. 1, shows a solenoid, hammer, anvil, and end cap;

FIG. 3 is a side view of the hammer of the impactor;

FIG. 4 is a side view of a second alternative embodiment of a paste feeder; and

FIG. 5 is a side view of a third alternative embodiment of a paste feeder.

DETAILED DESCRIPTION

U.S. Pat. No. 5,711,866 to Lashmore, which is hereby incorporated by reference, is a process for providing a mercury-free in situ dental restoration. The process uses hand pressure to condense paste of gold, silver or silver alloys and an activation solution of dilute 2% tetrafluoroboric acid. The tetrafluoroboric acid is a flux to remove the oxide during condensation, enabling the silver particles to cold weld to each other. Concentrations of the activation solution range from 0.5% to about 10%; an optimal concentration is about 2%. Particle sizes range from about 5 microns to about 50 microns. Both the silver and gold powders or foils are well annealed. The process offers a low cost, superior alternative to mercury-containing restorations. The principal drawbacks are the time required to install the restoration, the low density of the restoration when installed by hand instruments, and the need to remove the activation solution during the condensation.

The present invention addresses and resolves these drawbacks. An impactor 10 according to the present invention is shown in FIG. 1. The impactor 10 has a handle 20 and a head 30. The handle 20 has a cavity 40 for receiving a removable paste cartridge 22. The paste cartridge 22 holds paste and is either disposable or reusable. The paste cartridge 22 is pressurized as described below. In the disposable embodiment, the paste cartridge 22 is preferably heat sealed for long-term storage, and both ends of the paste cartridge 22 are cut open prior to insertion into the cavity 40 of the handle 20 or other paste feeding system.

The paste preferably has a combination of silver and activation solution. In the preferred embodiment, the activation solution is dilute 2% tetrafluoroboric (HBF₄) acid. Alternatively, the paste has a silver alloy or gold alloy. Gold foil combined with the activation solution may be used in lieu of the paste but would require hand placement. The resultant silver, gold-alloy powder, or gold foil is condensed in the cavity of a patient's tooth. This technology is designed to repair the damage caused by decay or corrosion of existing fillings.

The paste is fed into the cavity of the patient's tooth with either a pneumatic or a mechanical feeder. In an exemplary embodiment, a paste feeder tube 24 is used to transport the paste from the paste cartridge 22 to a paste dispensing tip 15 which is located adjacent to an anvil 32 which extends from the head 30. The paste feeder tube 24 may extend along, in, or be integral to, the handle 20. When the paste feeder tube 24 extends along the handle 20 and the head 30, grooves (not shown) on the exterior of the handle are used to receive and secure the paste feeder tube 24 thereto. Clips (not shown) could be used in lieu of the grooves. When assembled, the paste cartridge 22 and paste feeder tube 24 are sealed, creating a pressurized capsule. The paste is forced from the paste cartridge 22 through the paste feeder tube 24 to the paste dispensing tip 15 via a pneumatic supply source (not shown). The supply source, known to those having ordinary skill in the art, is operatively attached to the paste cartridge 22 and/or paste feeder tube 24 via a pneumatic control valve 53 or other similar means. The pneumatic control valve 53 controls the flow of air in the paste feeder tube 24. The dental practitioner uses the pneumatic control valve 53 to control the air pressure from the supply source to urge or force the paste from the paste cartridge 22 to the anvil tip 32 a and ultimately into the cavity of the patient's tooth. This valve 53 is preferably located on the handle 20 of the device. The valve 53 could also be a foot activated valve.

In a first alternative embodiment, the paste feeder tube 24 is operatively connected to an external source of paste material instead of the paste cartridge 22. In a second alternative embodiment, a mechanical paste feeder 50, FIG. 4, is used to allow preliminary condensation of the paste prior to contact by the anvil 32. A spring 51 pushes a plunger 54, which forces a certain amount of the paste, as determined by the operator, into the paste feeder tube 24. An ejector pin 52 forces the paste in the feeder 50 into the cavity of the patient's tooth and applies pressure onto the dispensed paste until the operator starts the condensation process. The mechanical paste feeder 50 delivers the same amount of material each time it is activated, pre-compacts the paste, and eliminates the need for a pneumatic supply source.

The head 30 has a housing 35 made of a corrosion-resistant material, such as nonmagnetic stainless steel, preferably 316 stainless steel, or a polymer such as Teflon®, nylon, or Vespel®. The housing 35, FIG. 2, has a diameter of approximately 0.5 of an inch, and a height of approximately 0.75 of an inch although such dimensions are not a limitation to the present invention. The housing 35 has an opening 42 for receiving the anvil 32 and a threaded hole 59 for receiving a set screw 41. The set screw 41 is used to hold the anvil 32 in place during use and to release the anvil 32 during non-use. One of the ends of the set screw 41 almost contacts the anvil 32 between stops 58. The anvil 32 is allowed to move vertically while the set screw 41 and the stops 58 limit the vertical movement. There are other devices for holding and releasing the anvil 32, such as a spring clip (not shown), which can be substituted for the set screw 41. The set screw 41 or spring clip allows efficient removal of the anvil 32 and other parts of the impactor 10 for cleaning and sterilization.

The anvil tip 32 a may be flat, serrated, rounded, concave, or shaped in any other configuration desired by the dental practitioner to access portions of the cavity that are difficult to reach. The anvil tip 32 a directly contacts the paste or filling material during impaction. The anvil tip 32 a may have a smaller diameter than a remaining portion of the anvil 32 and thus may form a small ledge near a bottom of the anvil 32, which acts as a pump to help move the paste to the anvil tip 32 a.

The solenoid 31 is operatively mounted between an end cap 49 and the housing 35. In one embodiment, the solenoid 31 is bonded into the housing 35. The solenoid 31 generates impact energy which is small but powerful. Alternatively, the impact energy is generated by a piezoelectric transducer, a magnetostrictive transducer, an electrostatic transducer, a small electric motor driving a cam, or a pneumatic transducer. Other solenoids that are known by those having ordinary skill in the art include full conical, tapered plunger, and cylindrical magnet types. Herbert C. Roters, Electromagnetic Devices, 1^(st) ed., John Wiley and Sons Inc., New York, 1941, p. 228, which is hereby incorporated by reference, describes some of these devices. The static force is about 8 pounds and the impact force is about 16 pounds. The frequency varies from 5 hertz (Hz) to 20 Hz, preferably around 8 Hz to 10 Hz.

In the preferred embodiment, a solenoid control unit (not shown) is operatively connected to the solenoid 31. The solenoid control unit provides current pulses for controlling the solenoid 31.

A constant current waveform is used to drive the solenoid 31. The waveform frequency varies from approximately 5 Hz to approximately 20 Hz. In the preferred embodiment, the waveform frequency is approximately 10 Hz. A pulsed current is ideally timed to turn on when a hammer 33 is furthest from the top surface 44 of the solenoid 31; however, a free running waveform is also possible. This waveform is preferably a square wave; however, the waveform can be sinusoid. A 110V ac driven system and battery driven system can be substituted for the constant current waveform.

The solenoid 31 includes a stator 31 a. The stator 31 a is made from a soft magnetic material such as a silicon iron alloy. The stator 31 a has a coil pocket with a preformed copper coil capable of supporting approximately 200 amp turns. Alternately, the stator 31 a may be made of an encapsulated soft magnetic material such as Somalloy 500 (from Haganous in Sweden). The preformed copper coil is injection molded and sealed so that the entire unit can be taken apart and sterilized.

The hammer 33 includes portions 45 and 46 made from a hardened steel, steel, or preferably Inconel®. Bonded to the horizontal portion 45 of the hammer 33 is a top surface 44. The top surface 44 is made of a soft magnetic material such as 2.5% SiFe, silicon iron alloys, phosphorus-containing iron alloy, nickel, chromium, iron alloy, iron polymer composite, iron-inorganic coated composites, iron phosphorus, or iron aluminum alloy. The hammer 33 is “T” shaped in the preferred embodiment as shown in FIG. 3. The hammer 33 has a horizontal portion 45 and a vertical portion 46. In the preferred embodiment, the horizontal portion 45 is an Inconel® disk integrated with the vertical portion 46 and machined out of a single piece of Inconel® to which the soft magnetic disk is bonded.

A bottom surface of the horizontal portion 45 is above the top surface 44 of the solenoid 31, shown in FIG. 2. The solenoid 31 has a slot 47 and an inner surface of the slot 47 has a sleeve bearing 34 thereon. The sleeve bearing 34 of the slot 47 receives the vertical portion 46 of the hammer 33. The vertical portion 46 extends beyond the bottom surface 43 of the solenoid 31 and is used to strike or contact the anvil 32. The vertical portion 46 of the hammer 33 slides up and down in the sleeve bearing 34 of the slot 47. The sleeve bearing 34 can be made of any suitable material, such as a phosphorous bronze or polytetraflouethylene (PTFE or Teflon®). The vertical portion 46 of the hammer 33 is in contact with a top surface 48 of the anvil 32.

The hammer 33 is forced downward by a magnetic attraction created by the solenoid 31. When the hammer 33 is forced downward by the solenoid 31, the vertical portion 46 of the hammer 33 strikes the anvil 32, thereby driving the anvil 32 into the paste. The solenoid 31 has a static force of about 8 pounds at contact. The hammer 33 moves upward because of the elastic rebound following the collision with the anvil 32. The rebound from this impact serves as a return spring.

When the hammer 33 moves up and down in the sleeve bearing 34 of the slot 47, the hammer 33 moves a vertical distance between approximately 0.010 to 0.040 of an inch. In the preferred embodiment, the hammer 33 moves a vertical distance of approximately 0.020 of an inch. The hammer 33 is restricted in its downward movement by the top surface 48 of the anvil 32 and in its upward movement by the end cap 49. The hammer 33 drives the anvil 32, thereby providing impulse loading to a silver powder in the paste, which was previously fed through the paste feeder tube 24 to the cavity in the patient's tooth, causing it to cold weld together into a dense filling.

The end cap 49 is removably mounted to the housing 35. In the preferred embodiment, the end cap 49 is screwed onto the housing 35. The end cap 49 and the housing 35 have mating threads. In an alternative embodiment, the end cap 49 is fastened to the housing 35 with spring clips (not shown).

A power supply (not shown) is used to give the dental practitioner the ability to independently control the force and the frequency of the impact of the anvil 32 by providing a series of current (voltage) pulses that periodically turn the electromagnet of the solenoid 31 on and off.

The power supply is a free running square wave current source or waveform synchronized with the position of the hammer 31, thereby turning on the current when the hammer 31 is furthest from the top surface 44 of the solenoid 31. The frequency ranges from 5 Hz to 20 Hz, preferably around 10 Hz. The current waveform is approximately a square-wave and is achieved by rapidly switching a constant current power supply at the desired frequency. Both the magnitude of the current and the frequency can be varied. It is possible to drive the solenoid 31 with a constant voltage waveform.

The frequency of this current waveform varies from approximately 5 Hz to approximately 20 Hz. The most desirable frequency is approximately 10 Hz, although this device can operate at frequencies up to 1000 Hz. A 110V ac driven system or a battery driven system can be used to drive the solenoid 31.

A suction tube 37 has a first end 37 a operatively attached to the housing 35 and a second end operatively attached to a vacuum system 36. The vacuum system 36 is preferably a continuously operating system. The suction tube 37 has a hollow core for removing liquids, semi-liquids, solids, and foreign matter from the patient's mouth. The first end 37 a of the suction tube 37 is proximate to the anvil tip 32 a of the anvil 32. The vacuum system 36 creates suction or a vacuum for removing the activation solution of the paste once the silver is condensed.

A separate vacuum system (not shown) known to those having ordinary skill in the art can be used for removing the patient's saliva, paste, particles from the removed filling, and other matter from the patient's mouth.

The external parts of the impactor 10 are stainless steel or as otherwise indicated herein, and the internal parts are removable for sterilization.

In an alternative embodiment, the impactor 10 is also used for cold welding, including solder bonding with pure silver or pure gold, thereby eliminating lead from the workplace and the undesirable side effects of tin, such as whisker formation and inter-metallic development.

In another alternative embodiment, the impactor 10 is scaled up to approximately 15 inches or greater in diameter and used to compact metal powders in a powder metallurgy die. The effective stress under the anvil 32 is greater than a factor of two and greater than the static stress under the solenoid 31, thereby magnifying the compaction and increasing density. For example, if the solenoid 31 is increased to 20 inches in diameter, the solenoid 31 will produce a compaction stress of over 14 tons. This compaction could then be repeated as often as required to obtain the required density.

The impactor 10 is assembled by placing the anvil 32 in the opening 42 of the housing 35. The anvil 32 is secured to the housing 35 via the set screw 41. One of the ends of the set screw 41 contacts the anvil 32 between the stops 58. The anvil 32 is allowed to move vertically but the set screw 41 and the stops 58 limit the vertical movement. The solenoid 31 is placed on the anvil 32 so that the slot 47 receives the top portion 48 of the anvil 32. The vertical portion 46 of the hammer 33 is placed through the slot 47 having the sleeve bearing 34 and rests on the top portion 48 of the anvil 32. The end cap 49 is secured to the housing 35.

To operate the impactor 10, one or more of the ends of the paste cartridge 22 are cut, and the paste cartridge 22 is placed into the cavity 40 of the handle 20. The solenoid 31 is periodically activated via the power unit or pneumatic control unit. When the solenoid 31 is activated, the hammer 33 is forced downward by a magnetic attraction created by the solenoid 31. When the hammer 33 is forced downward by the solenoid 31, the vertical portion 46 of the hammer 33 strikes the anvil 32, thereby driving the anvil 32 into the paste. The periodic impulse causes a high contact stress sufficient to condense the layer of metal paste to a high-density metal suitable for dental restorations. After the collision between the hammer 33 and the anvil 32, the hammer 33 moves upward because of the elastic rebound. The rebound from this impact serves as a return spring. Layers of paste are impacted until the cavity in the patient's tooth is filled.

In a third alternative embodiment, a mechanical paste feeder 60, FIG. 5, is used to feed paste into the cavity of the patient. The mechanical paste feeder 60 provides an accurate application of the paste into the cavity of the patient's tooth. The operator squeezes the handle 62 in the direction of the arrow shown in FIG. 5. The handle 62 drives a plunger 64 forward, compressing the paste with the paste feeder tube 66. The compacted paste is forced out of an aperture at the tip 68 of the paste feeder tube 66. The plunger 64 has a saw tooth profile 69 that allows a racket 70 driven by the handle 62 to drive the plunger 64. The saw tooth profile 69 allows a predetermined amount of paste to be ejected from the paste feeder tube 66. The distance the plunger 64 is driven forward is controlled by the period of the saw tooth profile 69. For example, increasing the period of the saw tooth would increase the distance the plunger 64 is driven forward and hence eject a greater amount of paste from the paste feeder tube 66. The saw tooth profile 69 is not limited to having a constant period. The period of the saw tooth profile 69 may gradually decrease, providing the operator with decreasing amounts of paste for each squeeze of the handle as the cavity fills with paste.

Once the paste feeder tube 66 is empty, the mechanical paste feeder 60 may be reloaded with paste by the operator. The operator removes the tip 68 of the mechanical paste feeder 60. The tip 68 may be removable and coupled to the mechanical paste feeder by screwing off the tip 68 from threads on the paste feeder tube 66. The tip 68 may also be coupled to the paste feeder tube 66 using a variety of other coupling devices, for example, but not limited to a snap fitting or frictional fitting. Prior to adding paste to the paste feeder tube 66, the operator may press a release switch 72 and pull backwards on the rear end of the plunger 64, thus pulling the plunger to the rear and allowing room within the paste feeder tube 66 to add additional paste. The paste may be added to the paste feeder tube 66 via a cartridge or other device designed for handling the paste.

Once paste is added to the paste feeder tube 66, the tip 68 is coupled back onto the mechanical paste feeder 60. The operator may squeeze the handle 62 initially to advance the plunger 64 forward and compact the paste within the paste feeder tube 66. A pistol grip may be used to allow the operator to ergonomically hold the mechanical paste feeder 60 and position the tip 68 into the cavity of the patient's tooth. The operator squeezes the handle 62 allowing the plunger to ratchet forward and drive the paste within the paste feeder tube 66 out of the aperture. As previously discussed, the saw tooth profile 69 provides a precise amount of ejected paste. A spring 74 may be used to drive the ratchet 70 and handle back into position, thereby allowing the operator to repeatedly squeeze the handle and provide additional precise amounts of ejected paste into the cavity.

Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention. 

1. A pneumatic paste feeder for moving paste, comprising: a paste source for holding paste; a paste feeder tube operatively connected between the paste source and a dispensing tip; and a pneumatic supply source for moving the paste from the paste source to the dispensing tip.
 2. The pneumatic paste feeder for moving paste according to claim 1, wherein said paste source includes a disposable paste cartridge.
 3. The pneumatic paste feeder for moving paste according to claim 1, wherein the paste comprises a material selected from the group consisting of silver, silver alloys, gold, and gold alloy powder in paste form to which is added 2% HBF₄.
 4. The pneumatic paste feeder for moving paste according to claim 1, further including a vacuum system for removing liquids, semi-liquids, and solids from a cavity of a patient's tooth.
 5. The pneumatic paste feeder for moving paste according to claim 1, further including a pneumatic control valve for controlling the flow of paste.
 6. A mechanical paste feeder for moving paste prior to impaction, comprising: a paste cartridge for holding a paste; a paste channel defining a cavity for holding the paste cartridge; a paste feeder tube, operatively connected between the paste channel and a dispensing tip; and a ratcheting device operatively connected to a plunger, for moving the paste from the paste cartridge through the paste feeder tube to the dispensing tip in controlled incremental amounts.
 7. The mechanical paste feeder according to claim 6, wherein the paste comprises a material selected from the group consisting of silver, silver alloys, gold, and gold alloy powder in paste form to which is added 2% HBF₄.
 8. The mechanical paste feeder according to claim 6, further including a vacuum system for removing liquids, semi-liquids, and solids from a cavity of a patient's tooth.
 9. The mechanical paste feeder according to claim 6, wherein said paste cartridge is a disposable paste cartridge.
 10. A mechanical paste feeder for moving paste, comprising: a paste cartridge for holding a paste; a paste channel defining a cavity for holding the paste cartridge; a paste feeder tube, operatively connected between the paste channel and a dispensing tip; and a displacement apparatus, coupled to the paste channel and the paste feeder tube, for moving the paste from the paste cartridge to the dispensing tip via the paste feeder tube in controlled, preselected amounts.
 11. The mechanical paste feeder according to claim 10, wherein the displacement apparatus includes a piston for displacing a controlled amount of paste to a cavity of a patient's tooth.
 12. The mechanical paste feeder according to claim 10, wherein the displacement apparatus includes a plunger for displacing a controlled amount of paste to a cavity of a patient's tooth.
 13. The mechanical paste feeder according to claim 10, wherein the paste comprises a material selected from the group consisting of silver, silver alloys, gold, and gold alloy powder in paste form to which is added 2% HBF₄.
 14. The mechanical paste feeder according to claim 10, further including a vacuum system for removing liquids, semi-liquids, and solids from a patient's mouth.
 15. The mechanical paste feeder according to claim 10, wherein the displacement apparatus is displaced by a constant amount and includes a piston displacing a constant amount of paste to a cavity of a patient's tooth.
 16. The mechanical paste feeder according to claim 10, wherein the displacement apparatus is displaced by a decreasing amount and includes a piston displacing a predetermined amount of paste to a cavity of a patient's tooth. 